Unified corrosion inhibitor



United States Patent 3,325,423 UNlilFiED (IQRRGSTQN INHIBITOR Charles18. Jordan, Aberdeen, Md, assignor to the United States of America asrepresented by the Secretary of the Army No Drawing. Filed .lune 24,1965, Ser. No. 466,866 7 Claims. (Cl. 252-389) The invention describedherein may be manufactured and used by or for the Government forgovernmental purposes, without the payment to me of any royalty thereon.

This application is a continuation-in-part of application, Ser. No.174,652, filed Feb. 20, 1962, for Multi purpose Corrosion Inhibitor, nowabandoned.

This invention relates to an improved corrosion inhibitor of thetetraborate type. More particularly, it relates to a novel tetraboratecomposition which provides improved corrosion inhibiting properties fororganic fluids such as hydraulic brake fluids, antifreeze compounds,shock absorber fluids, polar recoil oils and the like.

Hydraulic fluids, antifreeze compounds and other re lated fluids aregenerally corrosive to metals found in the brake and cooling systems ofvehicles. Due to the presence of a wide variety of metals which are tobe protected, the corrosion inhibitors employed are complex, highlycontrolled mixtures containing a large number of ingredients. Inhibitorsformulated for these systems as a rule contain one or more antioxidantsin combination with alkaline ingradients.

A particularly effective corrosion inhibitor for organic fluid has beendescribed in US. Patent 3,087,959, granted to me on Apr. 30, 1963,wherein the patented process is directed to the condensation reaction of1,2-propylene glycol with sodium tetraborate decahydrate. Thiscondensation reaction provided a considerably simplified and effectivecorrosion inhibiting additive in synthetic fluid media comprisingglycols and ethers of glycols. While this previous process has beenutilized to overcome the corrosive action of non-petroleum basehydraulic brake fluids and other synthetic type fluids, the condensateof said process was not suflicient without the contributory action of aphenolic or hydroquinone antioxidant. The prior art specification forinhibiting corrosion of the brake system metals, i.e., tin, steel,aluminum, cast iron, brass and copper was directed toward the combinedusage of the alkaline type tetraborate condensation product with asuitable antioxidant, as mentioned above.

The inclusion of antioxidants increases the complexity of hydraulicbrake fluids rendering such fluids more susceptible to interaction onprolonged storage or under various operating conditions. Antioxidantsseldom exhibit complete compatibility with synthetic fluids, and theyhave deleterious effects on natural or synthetic rubber components inbrake and cooling systems.

Further improvements in the tetraborate condensate are now possible inaccordance with the present invention that achieves in a unifiedtetraborate composition the alkaline action and the antioxidantproperties previously obtained by a combination of ingredients. Thenovel corrosion inhibitor of my present invention exhibits sufficientcorrosion inhibiting properties to be eflectively utilized as the soleinhibitor additive in synthetic fluids, such as the Ucons or othermixtures containing for example glycols, glycol-ethers, polyoxyglycols,castor oil and its derivatives, etc. Significantly, the present unifiedcorrosion inhibitor not only has eliminated the need for phenolic andother antioxidants previously required for adequate protection ofmetals, but the present unified composition displays increasedprotection to various metals.

Therefore, it is an object of the present invention to provide a novelcorrosion inhibitor which is capable of increased anticorrosionprotection to tin, steel, aluminum, cast iron, brass, copper or solderover other similar compositions used for this purpose.

Another object is to provide a novel tetraborate composition which isused efiectively as the sole inhibitor in fluids composed of glycols,glycol ethers and including such other materials as polyoxyglycols orcastor oil.

A further object is to provide a unified composition with enhancedproperties for protecting metals greater than the properties of theseparate constituents utilized in its synthesis.

A still further object resides in the process for forming a unified,stable composition which displays antioxidant properties and alkalineaction.

Yet a further object provides for improved hydraulic and coolant fluidswhich include an improved tetraborate composition to inhibit theircorrosive nature toward metals.

Other and further advantages of the present invention will becomeapparent from the following description and examples.

Thecorrosive inhibitor of this invention comprises the condensationproduct in which 1,2-propylene glycol is initially reacted with sodiumtetraborate decahydrate, and then by proper control of such reaction,2-hutyne-l,4-diol is reacted with the tetraborate. The finalcondensation product combines both the propylene glycol and theacetylenic diol to the tetraborate. By proper control of the reaction,it is possible to restrict the initial condensation to one or twomolecules of the glycol in order to involve the further condensationwith the unsaturated molecule.

The unified composition of the invention is produced by adding thetetraborate in increments to the "glycol at a temperature of C.i5 C. Ithas been found essential to add the tetraborate incrementally and toallow each increment to dissolve before further addition. A singleaddition of the tetraborate does not lead to the condensation reactionbut merely to a solution of borax in glycol. The total amount oftetraborate reacted with the glycol is about 20 to 30% by Weight of theglycol. After this addition is completed, the temperature of the mixtureis raised to C., and an amount of 2-b-utyne-1,4-diol equal to about theweight of the borate is added to the mixture. Heating is continued untilsubstantially all available Water is evaporated from the reaction.

The resulting liquid formed by the present reaction is clear, viscousand amber in color. A significant theoretical consideration of thepresent unified composition is its in-.

creased ability to provide protection to metal surfaces by a two-foldattack on the surrounding fluid media. The present condensate (1)initially sup-presses oxidation reactions in the surrounding fluid thatlead to acid formation and (2) effectively neutralizes any acids whichmay appear after a prolonged period of operation. Thus, the presentcomposition may be utilized as the sole corrosion inhibitor without theneed for blending various ingredients to provide corrosion protection tometals.

The present process and compositions will now be explained in greaterdetail by means of the following preferred embodiments thereof.

EXAMPLE I An amount of 1,2-propylene glycol weighing 700 grams washeated to a temperature of 85 C. with stirring. Powdered borax (sodiumtetraborate decahydrate) weighing 210 grams and amounting to 30% byweight of the glycol was added to the liquid in three equal increments,allowing sufticient time after each addition for the powder to dissolveand form a clear mixture. After the third increment of borax was added,the mixture was heated to 105 C. and maintained at that temperature forone hour with stirring. At this point, 2-butyne-1,4-diol weighing 140grams was added to the mixture, and the mixture was stirred at 105 C.for two additional hours. The resulting composition upon cooling wasclear, amber and viscous.

The condensate which is a preferred embodiment of the invention isproduced by reacting sodium tetraborate decahydrate with2-butyne-1,4-diol in a ratio of 3:2, respectively. Effective ranges inwhich the constituents may be combined in accordance with the inventionare expressed more conveniently in parts by weight:

Constituent: Parts by weight 1,2-propylene glycol 1.00 sodiumtetraborate decahydrate 0.2 to 0.3 2-butyne-1,4-diol 0.125 to :25

The inhibiting action of the present composition may be better explainedby observing the effect of its molecular structures. In the initialreaction of 1,2-propylene glycol with sodium tetraborate decahydrate,the following series of condensates will be formed:

This reaction can proceed as long as there are free OH groups and BO-Bbonds. In the present process, however, the time allowed for the initialcondensation with the 1,2-propylene glycol is carefully controlled tolimit the extend of condensation per molecule. By the time the2-butyne-1,4-diol is added, the sodium tetraborate molecule has acceptedonly one (illustrated by I above) or possibly two (illustrated by IIabove) of the 1,2-propylene glycol molecules. If the sodium tetraboratemolecule has accepted only one glycol molecule, the reaction with the2-butyne-1,4-diol would then yield the following product:

With two molecules of 1,2propylene glycol attached to the sodiumtetraborate, the reaction with Z-butyne-l, 4-diol would yield:

Again, the reaction of 2-butyne-1,4-diol with the molecules of sodiumtetraborate which have condensed with one or two 1,2-propylene glycolmolecules can proceed as long as free OH groups and BOB bonds arepresent. However, the condensation reaction depends on the length oftime at which the reaction ingredients are heated together. It isunlikely that the reaction proceeds far enough to form compounds otherthan those represented in reactions IV and V above. The contention thatfurther reactions are not involved in the present process is supportedby the fact that when heating is continued, solids begin to form in thereaction. This is in agreement with the theoretical aspects that furthercondensation would result in solid materials. The present condensationproduct is prepared in a manner in which the glycol and diol are reactedseparately at a temperature at which condensation proceeds repidly andthe water of the reaction is readily evaporated with a minimum loss ofglycol.

EXAMPLE II Sodium tetraborate decahydrate was added in severalincrements to 1,2-propylene glycol in a weight ratio of 1:5,respectively, while the mixture was being stirred and heated at C. Theaddition was carried out at a rate which avoids accumulation of solidsin the reaction mixture. Upon addition of the last amount oftetraborate,

the temperature was raised to 105 C. and the mixture was stirred forone'hour. An amount of 2-butyne-1,4-diol constituting /a the weight ofthe sodium tetraborate decahydrate was added to the mixture at 105 C.,and the mixture was continuously stirred and heated at 105 C. for anadditional two hours. This temperature was found to be suflicient forevaporation of the water of the reaction with a concomitant minimal lossof glycol. Also, this temperature is low enough to reduce thepossibility that volatile boron esters will form during the reaction.

The degree of condensation in this reaction may be determined by themethod disclosed in copending application, Ser. No. 332,557, filed Nov.8, 1963, which has issued as US. Patent 3,262,961 on July 26, 1966 toCharles B. Jordan, who is also the applicant herein, and wherein saidmethod is based on a Karl Fischer reagent which is employed as a testsolution to indicate the extent of water evaporated from the reaction.The reagent provides a convenient means for following the rate at whichwater is removed from the reaction and provides an accurate quantitativedetermination of the water content that remains in the condensationproduct. Normally, the heating step at 105 C. for two hours in an openvessel is suflicient to reduce the water content in the condensationproduct to a level of about 2.5%. Although, the water may be moredesirably reduced to a level of about 1.5%, prolonged heating to achievethis degree of dryness may result in excessive condensation andformation of solids.

EXAMPLE III The condensation product in accordance with the inventionmay be prepared from a sodium tetraborate having various degrees ofhydration. The procedure of the previous examples was repeated usingsodium tetraborate pentahydrate (30% by weight of the glycol). Theweight ratio of sodium tetraborate pentahydrate to Z-butyne-l, 4-diolwas 2:1, respectively. At the start, 5 moles of water were added to theglycol at 85 C. prior to the sodium tetraborate pentahydrate addition.

EXAMPLE IV A corrosion inhibitor in accordance with the invention mayalso be prepared using anhydrous sodium tetraborate. The addition ofmoles of water to the glycol at 85 C. before the tetraborate additionenables the reaction mixture to remain fluid and readily stirrablethroughout the reaction.

EXAMPLE V Condensation products in accordance with the reaction werealso prepared by substituting ethylene glycol for the 1,2-propyleneglycol in the process of Examples 1 and II. The tetraborate addition wason a by weight based on the weight of ethylene glycol, and the dioladdition was on an 18% by weight based on the weight of ethylene glycol.The product remained fluid throughout the reaction.

Test N0. 1

Corrosiveness of brake fluids is determined by testing metal strips ofthe six metals (tin, steel, aluminum, cast iron, brass and copper). Thetest specified in Military Specification MILH13910a involves cleanstrips of metal immersed in a brake fluid containing 3% of the presentcorrosion inhibitor by weight. The strips are kept in the fluid for 120hours at a temperature of 210:3 F. Following this test period, thestrips are then visually examined for evidence of corrosion, pitting,etching and discoloration. The strips are then weighed to the nearest0.1 milligram and the weight loss per unit area of each strip iscalculated. In order to pass the test satisfactorily, no pitting oretching should occur and very little discoloration of the strips ispermitted if the fluid is to be accepted for government use. The brakefluid in accordance with the aforementioned Military Specification whichis used to compare the effectiveness of corrosion inhibitors consists ofthe following composition:

Constituent: Percent by weight Butoxy polypropylene glycol 22.0Diethylene glycol monomethyl ether 35.0 Ethylene glycol monobutyl ether20.0 Ethylene glycol monoethyl ether 20.0

Corrosion inhibitor 3.0

The present corrosion inhibitor composition which Was tested in theabove brake fluid was prepared by reacting the following constituents inaccordance with the present process:

Constituent: Parts by weight 1,2-propylene glycol 1.00 Sodiumtetraborate decahydrate .30 2-butyne-1,4-diol .20

TABLE I Present Inhibitor Prior Art Inhibitor Metal Weight Weight VisualLoss Visual Loss Inspection (Milli- Inspection (Milligrams/ grams/ 0111.cm!) No change .00 N 0 change 00 .00 do .01 .01 d0 00 Brass Very slight06 stains. Copper Slight st;ains v 11 There was no pitting or etching,nor were there any deposits on the strips. The present corrosioninhibitor showed marked improvement with brass and copper. Weight losseswith the brass and copper metals were about three times higher with theprior art inhibitor.

The present inhibitor has been found effective when employed as anadditive in the range of 2.5-6% by weight.

Test N0. 2

In order to compare the improvement by the present unified corrosioninhibitor over a similar composition containing the same constituentsbut in separate form, the following test was devised:

The prior art condensate, employed in the previous test, was mixed withan equivalent amount of 2-butyne-1,4-dio1 to test the eflicacy of thecombination as a corrosion inhibiting composition. The procedure of theprevious test was employed, and the results obtained by this combinationof ingredients are now compared With the test results obtained with thepresent inhibitor.

The above test indicates that the mere presence of the acetyleniccompound does not provide the improvement which is achieved by combiningthe ingredients into a single inhibitor composition.

Test N0. 3

The stability of the present inhibitor in the brake fluid was alsotested. Strips of aluminum and cast iron, spaced .001 inch were insertedin the fluid and 2% benzoyl peroxide by weight was added. The fluid wasthen heated at 158 F. for 168 hours. The test revealed no weight loss toeither the aluminum or cast iron strip.

Antifreeze compounds are composed of diluted and undiluted glycols,alcohols and glycol-ethers. The present inhibitor was tested in anantifreeze solution made up of 50% glycol and 50% water by including ittherein in 3% by volume. The corrosiveness of the solution was thentested by metal strips (solder, steel, aluminum, cast iron, brass andcopper) which were immersed in the antifreeze solution at 180 F. for aperiod of 192 hours, during which time the antifreeze solution wasaerated and refluxed. After 192 hours the metal strips were removed fromthe solution, inspected and weighed. The results from this test arecompared in Table III with the performance of a standard antifreezesolution containing borax as the corrosion inhibitor.

Heavily stained. do-. Slightly stained. Cast iron Very slightly stainedDo.

The present inhibitor decreases corrosive action on all coolant systemmetals. It is especially beneficial to aluminum on which a protectiveoxide coating is readily formed which acts as a shield against corrosionand erosive action. The present unified inhibiting composition is alsocompatible with all present day antifreeze additives, such asmercaptobenzylthiazole and its salts, and they have no deleteriouseffects on the rubber components.

The present corrosion inhibitor is miscible in all proportions withwater. This is particularly desirable for organic coolants whether theyare diluted or undiluted. The inhibitor may also continue to protectbrake systems in which a large amount of water has accumulated.

The present condensate is substantially stable under prolonged storageand is not affected by a raise in temperature. Any oxidation ordecomposition of the organic constituents will be neutralized by thereserve alkalinity of the condensate. The stability of the triple bondexcludes attack by oxygen from the air, but permits attack of oxidationsoccurring in the liquid.

Thus it is apparent from the present specification that the novelcondensate of the present invention exhibits Slightly etched and pitted.

superior inhibiting properties against corrosion. It is also capable ofbeing utilized more effectively as the sole inhibitor in organic fiuidsthus allowing for greater stability and uniformity than the previousmixtures which were used for this purpose.

The invention is not limited to the specific examples and embodimentsherein disclosed, but includes all such modifications and adaptationsthereof made within the spirit of the invention as set forth in theappended claims.

Having particularly described this invention, that which is claimed is:

1. The process of preparing a corrosion inhibiting composition whichcomprises:

adding powdered sodium tetraborate decahydrate to 1,2-

propylene glycol at C. in increments in a total amount of about 20 to 30percent by weight of said glycol to form a solution,

heating said solution at about C. for about 1 hour,

adding 2-butyne-l,4-diol to said solution in an amount of about 12.5 to25 percent by weight of said glycol, and

heating the resulting solution at about 105 C. to evaporate the water ofthe reaction to a level of about 1.5-2.5 percent by weight of saidsolution.

2. The process of preparing a corrosion inhibiting composition inaccordance With claim 1 in which the resulting solution is heated at 105C. for a period of two hours.

3. A corrosion inhibiting composition prepared by the process of claim1.

4. The process as set forth in claim 1 wherein the sodium tetraboratedecahydrate is added in about 30 percent by weight of said glycol andsaid 2-butyne-l,4-diol is added in about 20 percent by weight of saidglycol.

5. A corrosion inhibiting composition prepared by the process of claim4.

6. A corrosion inhibiting composition prepared by the process of claim 1wherein said 2-butyne-l,4-diol is added in an amount equal to about /3the weight of said tetraborate.

7. The process of preparing a corrosion inhibiting composition whichcomprises:

adding to 1,2-propylene glycol an amount of water corresponding to(lO-n) times the molar equivalent of sodium tetraborate to be added insaid process, where n represents the molar ratio of the water ofhydration associated with said sodium tetraborate and is a number lessthan 10 and which may be zero,

heating said 1,2-propylene glycol and water to 85 C.

adding in increments said sodium tetraborate in a state of hydrationcorresponding to the formula References Cited UNITED STATES PATENTS2,979,524- 4/1961' Wright et a1 25275 2,982,733 5/l96 1 Wright et al252-75 3,087,959 4/1963 Jordan 260462 LEON D. ROSDOL, Primary Examiner.

SAMUEL H. BLECH, Examiner.

S. D. SCHWARTZ, Assistant Examiner.

7. THE PROCESS OF PREPARING A CORROSION INHIBITING COMPOSITION WHICHCOMPRISES: ADDING TO 1,2-PROPYLENE GLYCOL AN AMOUNT OF WATERCORRESPONDING TO (10-N) TIMES THE MOLAR EQUIVALENT OF SODIUM TETRABORATETO BE ADDED IN SAID PROCESS, WHERE N REPRESENTS THE MOLAR RATIO OF THEWATER OF HYDRATION ASSOCIATED WITH SAID SODIUM TETRABORATE AND IS ANUMBER LESS THAN 10 AND WHICH MAY BE ZERO, HEATING SAID 1,2-PROPYLENEGLYCOL AND WATER TO 85*C. ADDING IN INCREMENTNS SAID SODIUM TETRABORATEIN A STATE OF HYDRATION CORRESPONDING TO THE FORMULA